Metal substances are natural components of the earth and exist in many forms - each with its own specific chemical characteristics that define its interactions with the environment and with living organisms. Traditionally, most risk assessments and consequently guidance materials have focussed on organic chemicals. In many cases such guidance fails to adequately address specific characteristics that must be considered to perform accurate risk assessments for metal substances regarding Human Health.
Response to exposure to inorganic metal substances may vary with age, gender, pregnancy status, nutritional status and genetics. Diet plays an important role in oral exposure to metal substances, and there is a wide variability in the dietary intake of some metal substances depending on where people live. This means that a risk assessment in one region or even sub-region, may come up with different results compared to the same risk assessment in another region because dietary exposure can be influenced by geographic (presence of metal substances in water, soil, plants, …) and/or cultural variability.
Both the exposure route (inhalation, dermal, oral) and the physical and chemical form of a metal (powder, massive, metallic, oxidic, water-soluble, water-insoluble) can affect the metal’s potential to cause toxicity.
Clearly not all metal substances have the same essentiality/toxicity profiles. Differences in toxicokinetics can determine which organs receive higher metal doses and, in some cases, where the metal substances may accumulate.
Different metal substances may have different physico-chemical characteristics resulting in differing toxicity profiles, although for some specific endpoints metal substances may be similar.
Finally, it has to be taken into account that in some cases non-essential metal substances can compete with essential elements to cause toxicity. For instance, certain forms of lead (a non-essential metal for humans or animals) compete with calcium (an essential element) in the bone thereby leading to less calcium being incorporated, which in turn can cause osteoporosis.